At high power the LM4651/52 seems to be going into some protection mode?
If driving a load that is smaller than 4Ω the current limit protection may be turning on at higher output power levels. The current limit set by RSCKT is the sum of the peak output current in the load and the ripple current in the inductors. For a 4Ω load and 125W output the peak current in the load is 7.9 amps. The ripple current is affected by the inductor value, supply voltage and switching frequency. Some head room in the current limit should be designed in when setting the value of RSCKT. Normally RSCKT is set to 100kΩ giving 11Amps of output current. Lowering this resistor will increase the peak output current allowed from the FETs. This symptom can also be due to noisy or low supply lines. Under voltage detection is activated when either supply is within 10.7 Volts of GND. If the supply is unregulated and momentarily droops near this level UVD may be activated unintentionally. Increasing the capacitors on the supply lines will often solve this problem.
